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Abstract:

The present invention reduces the manufacturing cost of an eccentric
oscillating type speed reducer 11 while preventing the torque
transmitting capability of the eccentric oscillating type speed reducer
11 from being degraded.
A part of a case 12, which is in a meshing region 50 in which internal
teeth of the case 12 mesh with external teeth of pinions 20, is enabled
to bend in a direction in which the radius of curvature thereof
decreases. Thus, even when the concentration of a meshing load on the
vicinity of a part, at which the manner of meshing between the internal
teeth and the external teeth most differs from an ideal manner in the
meshing region 50, a part of the case 12, which is in the vicinity of the
part, bends in a direction in which the radius of curvature decreases.
Consequently, the meshing load can be uniformized by being dispersed in
the circumferential direction of the case 12.

Claims:

1. An eccentric oscillating type speed reducer comprising: a case with the
inner periphery of which a large number of internal teeth are formed
integrally, a carrier capable of performing relative rotation with
respect to said case, a pinion supported by said carrier and configured
so that external teeth meshing with said internal teeth are formed on an
outer periphery thereof, and a crank shaft which has an eccentric portion
inserted into said pinion and which rotates to cause said pinion to
perform eccentric rotation, wherein apart of said case, which is in a
meshing region in which said internal teeth mesh with said external
teeth, is enabled to bend in a direction in which a radius of curvature
thereof decreases.

2. The eccentric oscillating type speed reducer according to claim 1,
wherein said internal teeth are constituted by teeth having a circular
arc tooth profile, and where said external teeth are constituted by teeth
having a trochoidal tooth profile.

3. The eccentric oscillating type speed reducer according to claim 1,
wherein a seal member is interposed between the inner periphery of said
case on axial one side of said pinion and the outer periphery of said
carrier, wherein a bearing is interposed only between the inner periphery
of said case on the axial other side of said pinion and the outer
periphery of said carrier, and wherein said bearing causes said case and
said carrier to perform relative rotation.

4. The eccentric oscillating type speed reducer according to claim 3,
wherein an outside diameter of said bearing is set to be less than a
diameter of an addendum circle of said internal teeth.

5. The eccentric oscillating type speed reducer according to claim 4,
further comprising a pair of endplates respectively disposed on both
axial outer sides of said pinion, and bolts which fasten said end plates
to each other by being inserted into both of said end plates from one
axially side to the axially other side.

6. A rotation apparatus for a stabilizer shaft using an eccentric
oscillating type speed reducer, comprising said eccentric oscillating
type speed reducer according to claim 1, and a drive motor configured to
give a torque to a crank shaft of said eccentric oscillating type speed
reducer, and characterized in that a first stabilizer element
constituting one side of a stabilizer shaft is fixed to said case of said
speed reducer, while a second stabilizer element constituting the
remaining one side of said stabilizer shaft is fixed to said carrier of
said speed reducer.

7. The rotation apparatus for a stabilizer shaft according to claim 6,
wherein an attaching flange, to which said drive motor is attached, is
attached to said case, and wherein said first stabilizer element is fixed
to said case via said attaching flange by fixing said first stabilizer
element to said attaching flange.

Description:

TECHNICAL FIELD

[0001]The present invention relates to an eccentric oscillating type speed
reducer that reduces a speed of an input rotation, and to a rotation
apparatus for a stabilizer shaft, which uses the eccentric oscillating
type speed reducer.

BACKGROUND ART

[0002]As a conventional eccentric oscillating type speed reducer, for
example, the following speed reducer described in JP-B-5-86506 is known.

[0003]This speed reducer has a case provided with internal teeth by
impacting substantially half of each of a large number of cylindrical
pins into the inner periphery thereof, a carrier inserted into the case
so as to be able to perform relative rotation with respect to the case, a
pinion supported by the carrier so as to have external teeth formed on
the outer periphery thereof to mesh with the internal teeth, and a crank
shaft configured to have an eccentric portion inserted into a central
portion of the pinion and to rotate to cause the pinion to perform
eccentric rotation.

[0004]In recent years, such a speed reducer has been required to reduce
the manufacturing cost thereof without reducing a transmitted torque.
However, in a case where the internal teeth are constructed by impacting
the cylindrical pins into the case, as described above, the number of
components is increased. In addition, a process of impacting the pins
into pin grooves formed in the case is required. Consequently, the
manufacturing cost is high. Thus, it is considered to reduce the
manufacturing cost by forming the internal teeth integrally with the
case, by cutting work, precision casting, or the like, and by using
internal and external teeth with low machining accuracy. Also, a heat
treatment distortion of tooth portions (the internal teeth, and the
external teeth) is eliminated, and the manner of meshing between the
internal teeth and the external teeth is improved to an ideal manner by
polishing processing on the tooth portions after the tooth portions are
hardened by performing heat treatment processing thereon. Also, it is
considered to reduce the manufacturing cost of the speed reducer by
omitting the polishing processing for eliminating the distortion.

DISCLOSURE OF THE INVENTION

Problems that the Invention is to Solve

[0005]However, in the case of using the aforementioned internal and
external teeth with low machining accuracy or the internal and external
teeth, which are formed by omitting the polishing processing for
eliminating the heat treatment distortion, in the eccentric oscillating
type speed reducer, the concentration of a large meshing load on the
vicinity of a part, at which the manner of meshing between the internal
teeth and the external teeth largely differs from an ideal manner, is
caused in a meshing region in which the inner teeth mesh with the
external teeth while a torque is transmitted. Consequently, the
conventional eccentric oscillating type speed reducer has a problem that
the torque transmitting capability of the eccentric oscillating type
speed reducer is largely reduced.

[0006]An object of the present invention is to provide an eccentric
oscillating type speed reducer that can be manufactured at low cost while
preventing torque transmitting capability thereof from being degraded,
and to provide a rotation apparatus for a stabilizer shaft, which uses
this eccentric oscillating type speed reducer.

Means for Solving the Problems

[0007]First, such an object can be achieved by an eccentric oscillating
type speed reducer which comprises a case with the inner periphery of
which a large number of internal teeth are formed integrally, a carrier
capable of performing relative rotation with respect to the case, a
pinion supported by the carrier and configured so that external teeth
meshing with the internal teeth are formed on an outer periphery thereof,
and a crank shaft which has an eccentric portion inserted into the pinion
and which rotates to cause the pinion to perform eccentric rotation. In
this eccentric oscillating type speed reducer, a part of the case, which
is in a meshing region in which the internal teeth mesh with the external
teeth, can bend in a direction in which a radius of curvature thereof
decreases.

[0008]Second, such an object can be achieved by a rotation apparatus for a
stabilizer shaft using an eccentric oscillating type speed reducer, which
comprises the aforementioned eccentric oscillating type speed reducer,
and a drive motor configured to give a torque to a crank shaft of the
eccentric oscillating type speed reducer. In this rotation apparatus, a
first stabilizer element constituting one side of a stabilizer shaft is
fixed to the case of the speed reducer, while a second stabilizer element
constituting the remaining one side of the stabilizer shaft is fixed to
the carrier of the speed reducer.

ADVANTAGES OF THE INVENTION

[0009]According to the present invention, a large number of the internal
teeth are formed integrally with the inner periphery of the case. A part
of the case, which is in a meshing region in which the internal teeth and
the external teeth of the pinions mesh with one another, is enabled to
bend in a direction which the radius of curvature decreases. Thus, when
the concentration of the meshing load on the part, in which the manner of
meshing between the internal teeth and the external teeth largely differs
from an ideal manner, is caused by the eccentric rotation of the pinion,
a portion of the case, which is in the vicinity of this part, bends
(consequently, the portion of the case swells radially outwardly) in a
direction in which the radius of curvature decreases. Accordingly, the
meshing load is uniformized by being dispersed in the circumferential
direction of the case. Thus, the manufacturing cost of the eccentric
oscillating type speed reducer can be reduced while the torque
transmitting capability is restrained from being reduced.

[0010]Further, in a case where the eccentric oscillating type speed
reducer is used in a limited narrow space, particularly, in a case where
the eccentric oscillating type speed reducer is used in the rotation
apparatus for the stabilizer shaft, the outside diameter of the eccentric
oscillating type speed reducer is a fairly small diameter, the polishing
processing of the internal teeth and the external teeth are difficult to
perform. However, according to the present invention, a part of the case,
which is in the meshing region, can bend in a direction in which the
radius of curvature decreases. Thus, upon completion of hardening
processing, such as heat treatment processing, of the tooth portions, the
meshing load is uniformized by being dispersed in the circumferential
direction of the case, even without performing polishing processing on
the external teeth. Consequently, the present invention can preferably be
used especially, in such a case.

[0011]Furthermore, the aforementioned internal teeth are constituted by
teeth having a circular arc tooth profile. In addition, the external
teeth are constituted by teeth having a trochoidal tooth profile. Thus,
the concentration of the meshing load can be mitigated. Also, the
eccentric oscillating type speed reducer can be manufactured at low cost.
Further, a seal member is interposed between the inner periphery of the
case at an axial one side of each pinion and the outer periphery of the
carrier. On the other hand, in a case where the bearing is interposed
only between a part of the inner periphery of the case, which is provided
at the axial other side of the pinion, and the outer periphery of the
carrier. The case and the carrier are caused by the bearing to perform
relative rotation. Thus, the carrier and the case are cantilevered.
Consequently, as compared with a case where the carrier and the case are
supported in a center impeller manner, and where the bearings are
interposed between the inner peripheries of the case, which are provided
at both axially outer sides of the pinion, and the outer periphery of the
case, the case is more likely to bend in a direction in which the radius
of curvature thereof decreases. Consequently, the concentration of a
meshing load can be more effectively constrained.

[0012]Further, the outside diameter of the bearing is set to be less than
the diameter of the addendum circle of the internal teeth. Consequently,
the thickness (radial thickness) of the case at the axial other side of
the two pinions, more specifically, that of the axial other side end
portion of the case can be increased. Accordingly, the support stiffness
of this part is increased. Thus, the strength of the eccentric
oscillating type speed reducer is increased. Furthermore, the
aforementioned carrier is configured to have a pair of end plates
disposed at both axially outer sides of the pinion and to have also bolts
that fasten the endplates by being inserted into both end plates from
axial one side to the axial other side. Thus, the assembly of the carrier
can be facilitated. Consequently, an eccentric oscillating type speed
reducer, which can easily be assembled, is implemented. Moreover, an
attaching flange, to which the drive motor is attached, is attached to
the case. In addition, a first stabilizer element is fixed to the
attaching flange. Thus, the first stabilizer element is fixed to the case
via the attaching flange. Consequently, a drive motor can easily be
attached to the attaching flange. Accordingly, the drive motor can easily
be incorporated into the rotation apparatus for the stabilizer shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a front cross-sectional view illustrating Embodiment 1
according to the present invention.

[0014]FIG. 2 is a cross-sectional view taken in the direction of arrows
I-I shown in FIG. 1.

[0018]The internal teeth 13 are constituted by a large number of convex
circular arc portions 14 which radially inwardly protrude and which have
outer contours of a predetermined radius of curvature, and a large number
of concave circular arc portions 15 each of which smoothly connects the
adjacent concave circular arc portions 14 and which are radially
outwardly dented. Consequently, the internal teeth 13 are constituted by
teeth having a circular arc tooth profile. Incidentally, the expression
"smoothly connect" means that two circular arc curves are connected to
each other so that the adjacent circular arc curves have contact with
each other, that is, the circular arc of the convex circular arc portion
14 and the circular arc of the concave circular arc portion 15 are
connected to each other so as to have one common point and as to share
one tangential line in common at this common point.

[0019]In the case 12, a plurality of (two in the present embodiment)
ring-like pinions 20 are axially arranged and accommodated. Outer teeth
21 constituted by a large number of teeth of a trochoidal tooth profile,
more specifically, an epitrochoidal tooth profile are formed on the outer
peripheries of these pinions 20. Incidentally, the number of the external
teeth 21 of the pinions 20 is less than that of the internal teeth 13 by
one or two, more specifically, only by one in the present embodiment.
Further, the external teeth 21 mesh with the internal teeth 13 in a state
in which these pinions 20 are inscribed in the case 12. However, the
maximum meshing portions (parts at which the depth of meshing is the
largest) of the two pinions 20 are shifted in phase by 180 degrees with
each other. Incidentally, in a case where the internal teeth 13 are
formed integrally with the case 12 as described above, the internal teeth
13 and the external teeth 21 come into slide-contact with each other.
Thus, sometimes, the internal teeth 13 and the external teeth 21 are
early worn away. Accordingly, the hardness of surfaces of the internal
teeth 13 and the external teeth 21 are made to be high by applying
ion-nitriding thereon. Further, each component of the eccentric
oscillating type speed reducer 11 is made of metal. More specifically,
the case 12 and the pinions 20 use structural alloys, such as carbon
steels for machine structural use and chrome molybdenum high-strength
steels.

[0020]Incidentally, the range of meshing in the circumferential direction
between the external teeth 21 and the internal teeth 13 (range where the
external teeth 21 and the internal teeth 13 mesh and transmit torque)
varies from 45 degrees to 180 degrees, preferably, from 80 degrees to 100
degrees. Further, preferably, the radius of curvature of the circular arc
tooth file of the internal teeth 13 (the convex circular arc portions 14)
ranges from 0.2 mm to 0.5 mm. The reasons are as follows. The machining
and the finishing of the internal teeth 13 are very difficult in a case
where the radius of curvature of the internal teeth 13 is less than 0.2
mm. On the other hand, in a case where the radius of curvature thereof
exceeds 0.5 mm, the Hertzian stress in the surfaces of the teeth
increases, so that the peeling of the surfaces of the internal teeth 13
and the external teeth 21 are liable to occur. Also, it becomes difficult
to set the number of the internal teeth 13 to be equal to or more than
120 without increasing the pitch diameter of each of the external teeth
21 and the diameter of a circle connecting the centers of the circular
arcs of the internal teeth 13. Consequently, a large speed reduction
ratio cannot easily be obtained.

[0021]In each of the aforementioned pinions 20, a plurality of (four in
the present embodiment) through holes 22, which axially penetrate
therethrough, are formed. Theses through holes 22 are arranged at uniform
intervals in the circumferential direction of each of the pinions 20.
Reference numeral 23 designates a carrier inserted into the case 12. This
carrier 23 has a pair of end plates 24 and 25 disposed at both axially
outer sides of the two pinions 20, in the present embodiment, one side
disk-like end plate 24 placed on one axial side of the two pinions 20,
and the other side end plate 25 placed on the other axial side thereof,
and a plurality of bolts 26 (the number of which is equal to that of the
through holes 22) that fasten both the end plates 24 and 25 to each other
by inserting the plurality of bolts 26 into both the end plates 24 and 25
from one axial side to the other axial side and by screwing the other
axial side portions thereof into the other side end plate 25.

[0022]Further, the carrier 23 has a plurality of, more specifically, in
the present embodiment, four cylindrical column members 27 extending
axially. These column members 27 are loosely fit into the through holes
22, respectively. The bolts 26 pass through in the column members 27,
respectively. Each of the column members 27 is sandwiched by the one side
end plate 24 and the other side end plate 25 from both axial sides by
screwing the bolts 26 into the other side end plate 25. The axial length
of each of the column members 27 is slightly longer than a total
thickness of the two pinions 20. Incidentally, although the column
members 27 are formed separately from both the end plates 24 and 25, the
column members can be formed integrally with the one side end plate or
with the other side end plate according to the present invention.

[0023]Reference numeral 31 designates an oil seal serving as a seal member
interposed between the inner periphery of the case 12 on axial one side
of the two pinions 20 and the outer periphery of the carrier 23, more
particularly, between the inner periphery of the axial one side end
portion 16 of the case 12 and the outer periphery of the one side end
plate 24. This oil seal 31 seals between the case 12 and the carrier 23
and prevents a lubricant agent or the like from leaking out from
therebetween and prevents also dust, dirt or the like from entering the
case 12. Reference numeral 32 denotes a couple of bearings interposed
only between the inner periphery of the case 12 on the axial other side
of the two pinions 20 and the outer periphery of the carrier 23, more
particularly, only between the inner periphery of the axial other side
end portion 17 of the case 12 and the outer periphery of the other side
end plate 25. The couple of bearings are disposed by being slightly
spaced from each other. These bearings 23 enable the case 12 and the
carrier 23 to perform relative rotation.

[0024]Both the end plates 24 and 25, the bolts 26, and the column members
27, which have been described above, in their entirety are inserted into
the case 12, and constitute the aforementioned carrier 23 capable of
performing relative rotation with respect to the case 12. Further, in a
case where the bearings 32 are interposed only between a part of the
inner periphery of the case 12, which is provided at the axial other side
of the two pinions 20, and the outer periphery of the carrier 23 in a
portion between the inner periphery of the case 12 and the outer
periphery of the carrier 23 as described above, the carrier 23 and the
case 12 are cantilevered. Thus, as compared with a case where the carrier
23 and the case 12 are supported in a center impeller manner, and where
the bearings 32 are interposed between the inner peripheries of the case
12, which are provided at both axially outer sides of the two pinion 20,
and the outer periphery of the case 12, the case 12 is more likely to
bend in a direction in which the radius of curvature thereof decreases.
Consequently, the concentration of a meshing load can be more effectively
constrained.

[0025]Further, the outside diameter of the bearings 32 is less than the
diameter of the addendum circle of the internal teeth 13. Consequently,
the thickness (radial thickness) of the case 12 at the axial other side
of the two pinions 20, more specifically, that of the axial other side
end portion 17 of the case 12 can be increased. Accordingly, a thick wall
part, whose inside diameter is less than the diameter of the addendum
circle of the internal teeth 13, is formed in the axial other side end
portion 17 of the case 12. The support stiffness of this part (part
abutting against the bearings 32 of the case 12) is increased. Thus, the
strength of the eccentric oscillating type speed reducer 11 is increased.

[0026]Then, in a case where the bolts 26 are inserted into both the end
plates 24 and 25 from axially one side to the axially other side, as
described above, the bolts 26 are less subjected to interference from the
bearings 32 which are relatively small in diameter. Thus, as compared
with a case where the bolts 26 are inserted into both the end plates 24
and 25 from the axial other side to the axial one side, the assembly of
the carrier 23 is easily achieved. Consequently, the manufacturing cost
of the eccentric oscillating type speed reducer 11 can be reduced.

[0027]Reference numeral 33 designates a plurality of (eight in the present
embodiment, which is a number that is twice the number of the through
holes 22) pin holes formed in each pinion 20, which extend axially. These
pin holes 33 are arranged pair by pair (two by two) between each adjacent
pair of the through holes 22 arranged in the circumferential direction of
each pinion 20. Reference numeral 34 denotes pins the number of which is
equal to that (eight) of the pin holes 33. An axially central portion of
each of such a plurality of pins 34 is loosely fit into an associated one
of the pin holes 33. On the other hand, both axial end portions of each
of the pins 34 are supported by the carrier 23. More particularly, both
axial end portions of each of the pins 34 are supported by and fixed to
the carrier 23 by being press-fit into both the end plates 24 and 25,
respectively.

[0028]Reference numeral 35 designates a ring rotatably fit onto the
axially central portion of each pin 34 so that the number of the rings is
equal to the number (two) of the pinions 20. The inside diameter of these
rings 35 is substantially equal to the outside diameter of each pin 34.
Thus, the inner periphery of the ring 35 comes into slide-contact with
the outer periphery of the pin 34. Further, the outside diameter of the
ring 35 is less than the inside diameter of the pin hole 33 by an amount
which is twice the eccentricity amount of an eccentric portion 43 of a
crank shaft 40, which will be described below. The outer periphery of the
ring 35 is in rolling contact with the inner periphery of the pin hole
33. Consequently, the pinions 20 are eccentrically rotatably supported by
the carrier 23 via the pins 34 and the rings 35.

[0029]Incidentally, each set of the aforementioned pin 34 and the
aforementioned ring 35 in their entirety is configured so as to be
inserted into an associated one of the pin holes 33 by engaging the
central part thereof with the associated one of the pin holes 33, as to
have both end portions thereof, which are supported by the carrier 23,
and as to constitute an engaging pin 36 which performs relative rotation
with respect to each pinion 20. Incidentally, according to the present
invention, in addition to the constituting of each engaging pin by
integrating each pin and the associated ring with each other, both axial
end portions of each engaging pin can be configured to be rotatably
supported by both the end plates, respectively. Alternatively, each
engaging pin can be constituted a pin with an eccentric portion by
omitting the rings. In addition, both axial end portions of each engaging
pin can be configured to be rotatably supported by both the endplates so
that the outer periphery of the eccentric portion is brought into slide
or rolling contact with the pinions (pin holes).

[0030]Reference numeral 40 designates one hollow crank shaft, which is
loosely fit into a crank shaft hole 39 formed on the central axis of the
carrier 23 and extends axially. This crank shaft 40 is such that both end
portions thereof are supported by the end plates. More particularly, one
end portion of the crank shaft 40 is rotatably supported by the one side
end plate 24 via a bearing 41, while the other end portion thereof is
rotatably supported by the other side end plate 25 via a bearing 42.
Further, this crank shaft 40 has two decentered eccentric portions 43 at
the central portion thereof. These eccentric portions 43 are arranged at
axial positions so as to overlap with the pinion 20. Moreover, these
eccentric portions 43 are shifted in phase only by 180 degrees.
Additionally, the eccentric portions 43 are inserted into a crank hole 44
formed in central portions of the pinions 20 so as to penetrate axially
therethrough in a state in which a cylindrical roller bearing 45 is
interposed therebetween. Further, when the crank shaft 40 rotates, the
pinions 20 eccentrically rotate.

[0031]Incidentally, preferably, the outside diameter of the cylindrical
roller bearing 45 is set to be within a range of 30% to 65% of the
diameter D of a circle connecting the centers of the circular arcs of the
internal teeth 13 of the case 12, more particularly, the diameter D of a
circle connecting the centers of curvature (the centers of circular arcs)
P of the convex circular arc portions 14. The reasons are as follows. In
a case where the outside diameter of the cylindrical roller bearing 45 is
less than 30% of the diameter D, the load capability of the cylindrical
roller bearing 45 is reduced, so that transmitted torque is reduced. On
the other hand, in a case where the outside diameter of the cylindrical
roller bearing 45 exceeds 65% of the diameter D, the diameter of the pins
34 is reduced. Alternatively, the radially thickness of a part of each of
the pinions 20, in which the pins 34 are inserted, is reduced. Thus,
similarly, there is a fear of reduction in the transmitted torque.
However, in a case where the outside diameter of the cylindrical roller
bearing 45 is set to be within the aforementioned range, such effects are
balanced. Consequently, the transmitted torque can have a large value.
Furthermore, it is more preferable that the outside diameter of the
cylindrical roller bearing 45 is set to be within a range of 40% to 60%
of the diameter D. This is because the aforementioned advantages can be
surely obtained.

[0032]Further, when drive rotation is input to the crank shaft 40, the
crank shaft 40 rotates around the axis of rotation thereof. Consequently,
the eccentric portion 43 of the crank shaft 40 rotates in the crank hole
44 of each of the pinions 20. The pinions 20 perform eccentric
oscillating rotations. At that time, the number of the external teeth 21
of the pinion 20 is less than that of the internal teeth 13 of the case
12 only by one. Thus, the speed of the relative rotation between the case
12 and the carrier 23 is considerably reduced, so that the case 12 and
the carrier 23 perform relative rotation at low speed. The case 12, the
pinions 20, the carrier 23, and the crank shaft 40 in their entirety,
which have been described, constitute the eccentric oscillating type
speed reducer 11 capable of reducing input rotation at a high ratio.

[0033]Incidentally, in a case where the machining accuracy of at least one
of a set of the internal teeth 13 of the case 12 and a set of the
external teeth 21 of the pinions 20 is low in the aforementioned
eccentric oscillating type speed reducer 11, and where polishing
processing for eliminating a heat treatment distortion is omitted, a
large meshing load is concentrated on the vicinity of a part, at which
the manner of meshing between the internal teeth 13 and the external
teeth 21 differs largely from an ideal manner, in a meshing region 50 in
which the internal teeth 13 mesh with the external teeth 21, while torque
is transmitted therebetween.

[0034]Thus, in the present embodiment, a part of the case 12, which is in
the meshing region 50 in which the internal teeth 13 and the external
teeth 21 of the pinion 20, is made to be thin, as compared with the
thickness of the conventional case, and is thus enabled to bend in a
direction in which the radius of curvature thereof is reduced.
Consequently, during a rated torque is transmitted, when the
concentration of a large meshing load on the vicinity of a part, at which
the manner of meshing between the internal teeth 13 and the external
teeth 21 differs largely from an ideal manner, is caused by the eccentric
rotation of each of the pinions 20 in the meshing region 50, a portion of
the case 12, which is in the vicinity of this part, bends in a direction
in which the radius of curvature thereof is reduced (consequently, this
portion swells radially outwardly). Accordingly, the meshing load is
uniformized by being dispersed in the circumferential direction of the
case 12.

[0035]As a result, the manufacturing cost of the eccentric oscillating
type speed reducer 11 can be reduced while torque transmitting capability
is restrained from being reduced. Further, in the present embodiment, the
internal teeth 13 are constituted by teeth having a circular arc tooth
profile, as described above. In addition, the external teeth 21 are
constituted by teeth having a trochoidal tooth profile. Thus, the
concentration of the meshing load can be further mitigated. Also, the
eccentric oscillating type speed reducer 11 can be manufactured at low
cost. Incidentally, because the case 12 is configured to be able to flex
(bend), as described above, it is preferable that the case 12 is made of
a material whose hardness and toughness are higher than those of the
pinions 20.

[0036]Further, in the present embodiment, in a case where a thickness from
the bottom of each of the internal teeth 13 to the outer periphery 51 of
the case 12 in the aforementioned meshing region 50 is set at the minimum
thickness T in the aforementioned meshing region 50, the meshing region
50 of the aforementioned case 12 is connected to the axial other side end
portion 17 by a thin wall portion 18 whose thickness is less than the
minimum thickness T. Consequently, the flexing (bending) of the case in
the aforementioned meshing region 50 is further facilitated. Furthermore,
in order to mitigate the concentration of stress, a circular arc portion
(R) R1 having a predetermined radius of curvature R1 is formed on the
border between the meshing region 50 and the thin wall portion 18, while
a circular arc portion R2 having a predetermined radius of curvature R2
is formed on the border between the thin wall portion 18 and the axial
other side end portion 17. Incidentally, the difference in thickness
between both sides of the latter circular arc portion R2 is larger than
that in thickness between both sides of the latter circular arc portion
R1. Thus, the radius R2 of curvature of the latter circular arc portion
is larger than that of curvature of the former circular arc portion.

[0037]Further, the former circular arc portion R1 is formed of the top
portion of the inner tooth 13. Therefore, burrs are prevented from being
produced when the internal teeth 13 are machined. Incidentally, the
aforementioned circular arc portions R1 and R2 can be formed by combining
a plurality of circular arcs that differ in radius of curvature from one
another. Furthermore, in order to flex (bend) the case 12, as described
above, in a case where the diameter D of a circle connecting the centers
of curvature (the centers of circular arcs) P of the convex circular arc
portions 41 exceeds 60 mm and is equal to or less than 100 mm, it is
sufficient to set the minimum thickness T to be within the range of 3% to
8% of the diameter D, preferably, 3% to 5% of the diameter D.

[0038]Moreover, in a case where the aforementioned diameter D exceeds 100
mm and is equal to or less than 200 mm, it is sufficient to set the
aforementioned minimum thickness T to be within the range of 3% to 7% of
the aforementioned diameter D, preferably, 4% to 6% of the diameter D.
Additionally, in a case where the aforementioned diameter D exceeds 200
mm and is equal to or less than 300 mm, it is sufficient to set the
aforementioned minimum thickness T to be within the range of 2% to 6% of
the aforementioned diameter D, preferably, 3% to 5% of the diameter D.
Further, in a case where the aforementioned diameter D exceeds 300 mm and
is equal to or less than 400 mm, it is sufficient to set the
aforementioned minimum thickness T to be within the range of 1% to 5% of
the aforementioned diameter D, preferably, 2% to 4% of the diameter D.
Thus, as described above, the case 12 can be bent, and the meshing can be
uniformized.

[0039]An example of the aforementioned eccentric oscillating type speed
reducer 11 is described hereinbelow. The outside diameter of the case 12
was 102.00 mm. Both of the diameter D of a circle connecting the centers
P of the circular arcs of the internal teeth 13 and the diameter of a
pitch circle of the external teeth 21 of each pinion 20 were 95.0 mm. The
diameter of the addendum circle of the internal teeth 13 was 94.10 mm.
The diameter of the root circle of the internal teeth 13 was 95.151 mm.
The diameter of the addendum circle and that of the root circle of each
pinion 20 were 94.48 mm and 93.72 mm, respectively. The radius of
curvature of the circular arc tooth profile of the internal teeth 13 was
0.45 mm. The pitch of the internal teeth 13 was 1.50 mm. The minimum
thickness T of the case 12 in the meshing region 50 is 3.425 mm (3.60% of
the diameter D). The number of the internal teeth 13 was 200. The number
of the external teeth 14 was 199. Further, in a case where a rated torque
was given to such an eccentric oscillating type speed reducer 11, an
amount of swelling radially outwardly was 20 μm when a part of the
case 12, which was in the meshing region 50, bent.

[0040]Reference numeral 53 is a substantially disk-like attaching flange,
which is attached to the other side surface (the other side surface of
the thick wall portion of the case 12) by being positioned with high
precision by smooth fitting. A drive motor 45 is attached to the radially
central portion of the other side surface of this attaching flange 53
with bolts 55. Consequently, this drive motor 54 is coaxially configured
with the crank shaft 40. An end portion of the rotating shaft 56 of this
drive motor 54 is inserted into and spline-connected to a hollow hole 57
of the crank shaft 40. Thus, the rotating shaft 56 of this drive motor 54
is connected (directly connected in the present embodiment) to the other
end portion of the crank shaft 40. Consequently, when the drive motor 54
operates, so that a torque is given to the crank shaft 40 from the
rotating shaft 56, the crank shaft 40 rotates around the axis of rotation
thereof.

[0041]Incidentally, the aforementioned eccentric oscillating type speed
reducer 11 and the drive motor 54 in their entirety constitute a rotation
apparatus 58 for a stabilizer shaft 61, which positively gives a torque
to the stabilizer shaft 61 against twist caused in the stabilizer shaft
61 (to be described below) based on roll. Reference numeral 60 designates
a first stabilizer element which constitutes one side portion of the
stabilizer shaft 61 provided in a vehicle in order to remain balance of a
vehicle (an automobile, a railway vehicle, or the like), and which is
coaxial with the central axis of the aforementioned eccentric oscillating
type speed reducer 11. The other end of this first stabilizer element 60
is connected to an arm (not shown) attached to a wheel (right wheel in
the present embodiment).

[0042]On the other hand, a bottomed cylindrical cover portion 62, which
moves in concert with the attaching flange 53 and surrounds the drive
motor 54, is formed at one end of the first stabilizer element 60
integrally therewith. This cover portion 62 is positioned at a radially
outer end portion of the other side surface of the attaching flange 53 by
smooth fitting. The cover portion 62 is fixed by being fastened together
with the attaching flange 53 and the case 12 by a bolt 63, one end of
which extends into the thick wall portion of the case 12. Consequently,
the first stabilizer element 60 is fixed to the case 12 via the attaching
flange 53. Thus, the drive motor 54 can easily be attached to the
attaching flange 53. Consequently, the drive motor 54 can easily be
incorporated into the rotation apparatus 58 for the stabilizer shaft.

[0043]Reference numeral 66 designates a second stabilizer element, which
constitutes the remaining one side of the aforementioned stabilizer shaft
61 and is coaxial with the central axis of the aforementioned eccentric
oscillating type speed reducer 11. One end of the second stabilizer
element 66 is fixed to an arm (not shown) attached to a wheel (left wheel
in the present embodiment). On the other hand, a disk-like portion 67 for
closing one end opening of a crank shaft hole 39 is formed at the other
end of the second stabilizer element 66 integrally therewith. The
disk-like portion 67 is fixed to one side surface of the carrier 23 with
a plurality of bolts 68. The positioning of these components is performed
by faucet connecting, by which the outer peripheral surface of a faucet
portion formed on the central portion of the other side surface of the
aforementioned disk-like portion 67 is brought into surface contact with
the crank shaft hole 39. Incidentally, the axially central portion of
each of the first stabilizer element 60 and the second stabilizer element
66 is rotatably attached to a vehicle via a bearing (not shown).

[0044]Incidentally, in a case where the eccentric oscillating type speed
reducer 11 is used in a limited space, such as the rotation apparatus 58
for the stabilizer shaft, the outside diameter of the eccentric
oscillating type speed reducer 11 is a fairly small diameter. Thus, the
polishing processing of the internal teeth 13 and the external teeth 21
is difficult to perform. However, in the present embodiment, a part of
the case 12, which is in the meshing region 50, can be bent in a
direction in which the radius of curvature thereof is decreased.
Accordingly, upon completion of performing hardening treatment, such as
heat treatment processing, on the teeth portions, the meshing load is
dispersed in the circumferential direction of the case 12 and is
uniformized when the pinions rotate, even without performing polishing
processing thereon. Thus, the aforementioned eccentric oscillating type
speed reducer 11 can be particularly suitably used in the rotation
apparatus 58 for the stabilizer shaft.

[0045]Incidentally, the rotation apparatus 58 and the stabilizer shaft 61
in their entirety are attached to a vehicle (not shown) and constitute an
active stabilizer apparatus 70 capable of positively giving a
counterbalancing force against roll, which is generated in the vehicle
mainly at the time of turning driving thereof, to the stabilizer shaft to
restrain the left and right wheels from moving in vertically opposite
phases. Additionally, such an active stabilizer apparatus 70 can be
mounted in one or both of front or rear portions of a vehicle.

[0046]Next, an operation of the aforementioned Embodiment 1 is described
below.

[0047]When a vehicle, to which the active stabilizer apparatus 70 is
attached, is caused to perform turning-driving, roll is generated in a
vehicle. At that time, the drive motor 54 is operated on the basis of,
for example, lateral G detected by a sensor (not shown), or the like.
When a torque is given to the crank shaft 40 from the rotating shaft 56
by operating the drive motor 54, the crank shaft 40 rotates around the
axis of rotation thereof. Consequently, the eccentric portion 43 of the
crank shaft 40 rotates in the crank hole 44 of each pinion 20 to cause
the pinions 20 to perform eccentrically oscillating rotations. However,
the number of the external teeth 21 of the pinion 20 is less than that of
the internal teeth 13 of the case 12 only by one. Thus, the speed of the
relative rotation between the case 12 and the carrier 23 is considerably
reduced, so that a rotation of the crank shaft 40 is transmitted to at
least one (both in the present embodiment) of the case 12 and the carrier
23. Consequently, the case 12 and the carrier 23 are caused to perform
relative rotation (reverse rotation) at low speed.

[0048]Accordingly, the first stabilizer element 60 fixed to the case 12,
and the second stabilizer element 66 fixed to the carrier 23 relatively
reverse rotation at low speed. As a result, a counterbalancing torque
against twist generated in the stabilizer shaft 61 based on roll is given
to the stabilizer shaft 61. Thus, the generation of roll is effectively
prevented. A vehicle, which is turning-driving, is held in a balanced
condition.

[0049]Incidentally, as described above, a large number of internal teeth
13 are integrally formed on the inner periphery of the case 12. In
addition, a part of the case 12, which is in the meshing region 50 in
which the aforementioned internal teeth 13 and the external teeth 21 of
the pinions 20 mesh, is enabled to bend in a direction in which the
radius of curvature decreases. Thus, even when the concentration of a
large meshing load on the vicinity of a part, at which the manner of
meshing between the internal teeth 13 and the external teeth 21 differs
largely from an ideal manner, is caused by the eccentric rotation of each
of the pinions 20 in the meshing region 50, a portion of the case 12,
which is in the vicinity of this part, bends in a direction in which the
radius of curvature thereof is reduced (consequently, this portion swells
radially outwardly). Accordingly, the aforementioned meshing load is
uniformized by being dispersed in the circumferential direction of the
case 12. Consequently, the manufacturing cost of the eccentric
oscillating type speed reducer 11 can be reduced while torque
transmitting capability is restrained from being reduced.

[0050]Further, in a case where the eccentric oscillating type speed
reducer 11 is used in a limited space, particularly, in the
aforementioned rotation apparatus 58 for the stabilizer shaft, the finish
polishing processing of the internal teeth 13 and the external teeth 21
is difficult to perform. However, the eccentric oscillating type speed
reducer 11 is such that a part of the case 12, which is in the meshing
region 50, can bend in a direction in which the radius of curvature
decreases. Thus, the meshing load is uniformized by being dispersed in
the circumferential direction of the case 12, even without performing
polishing processing on the internal teeth 13 and the external teeth 21.

[0051]Incidentally, in the aforementioned embodiment, the single crank
shaft 40 is disposed on the central axis of the eccentric oscillating
type speed reducer 11. However, according to the present invention, a
plurality of crank shafts can be disposed at a uniform distance from the
central axis of the eccentric oscillating type speed reducer 11 and at
uniform angular intervals, instead of the crank shaft 40. At that time,
the pinions are supported by the carrier via the plurality of crank
shafts.

[0052]Further, in the aforementioned embodiment, both the case 12 and the
carrier 23 are rotated. However, according to the present invention, the
case 12 and the carrier 23 can be configured so that one of the case 12
and the carrier 23 is fixed, while the remaining one of the case 12 and
the carrier 23 is rotated. Furthermore, in the aforementioned embodiment,
the internal teeth 13 and the external teeth 21 with low machining
accuracy are used. However, according to the present invention, teeth
with low machining accuracy can be used as one of a set of the internal
teeth 13 and a set of the external teeth 21. Alternatively, teeth with
high machining accuracy can be used as both the set of the internal teeth
13 and the set of the external teeth 21.

INDUSTRIAL APPLICABILITY

[0053]The present invention can be applied to an industrial field of an
eccentric oscillating type speed reducer configured to reduce a speed by
causing pinions to perform eccentric rotations using a crank shaft.